Given that Orac-dr is what you will use at the telescope, and that it provides the easiest introduction
to the various steps necessary to reduce your data, we will deal with it first. If you are at the
telescope log into mamo (if you are working on another machine just ssh mamo), and then
type:
Xoracdr gui for orac-dr. All the information needed to start the data reduction
(ie. where the data is, what instrument is being used, what ut date) is prompted for.If you are at your home institution or at the JAC, you should use the new x-windows gui. Simply type:
and the interface shown in Figure 1 should pop-up. Fill in the appropriate date, the location of the raw data files (see below if you are at the JAC and unsure) as well as where you want the reduced data to go, and press Start!
Having done one or other of the previous set-ups you should then find a dialogue window pops up,
with explanatory messages about what the pipeline is doing, followed shortly by a xwindow which
will display all the key stages of the reduction. You will find that Orac-dr starts working through the
observations one by one ignoring some (like the focus and align measurements) but reducing
most. For each distinct type of observation (pointing, skydip, jigglemap) Orac-dr has a
recipe it uses to reduce the data. If you miss a stage (maybe you went out to make a coffee)
or you want to examine something in detail, don’t despair look at the output directory
for the reduction, you will find many of the final reduced files and intermediate stages
eating into your disk space. From the name of the file you should be able to work out at
what stage of the reduction it was produced – the final ‘re-binned images’ should finish in
“_reb”.
Given this is a cookbook for reducing map data, let’s look at the two recipes for reducing jiggle-maps,
and emerson2 maps. You can find these by typing “ls $ORAC_DIR/recipes/SCUBA” (if the environment
variable is not set type “oracdr_scuba”). The jiggle map recipe reads,
while the scan map recipe reads (omitting the verbose header information),
Both read surprisingly like English, each line in the recipes is a step to be done in the data processing (or in the Orac-dr parlance a call to a ‘primitive’). Also it is worth noting that the first few steps are nearly identical. The pre-processing, flat-fielding, despiking and extinction correction is the same for both jiggle, and scan map data, they only differ in the despiking, removal of baselines and skynoise, and in the rebinning. Note many of the steps have variables which can be set to customize the recipe, i.e. N_SIGMA on the clipping, and PIXEL_SIZE in the rebinning. It is possible to accurately reduce your data using Orac-dr alone, using the supplied variables in the recipe, customizing the recipes to use the wide range of set primitives issued with Orac-dr or even by altering primitives or writing new ones (though this requires you to become acquainted with object-orientated Perl). At the very least Orac-dr should be run twice, once at the summit when the data is being taken, and once at home to give you something to compare to. However the next sections describe how to reduce the data at the ‘bare-bones’ level using Surf and the standard Starlink data-reduction packages.